Control apparatus for internal combustion engine

ABSTRACT

An engine ECU executes a program including the step of detecting engine start, the step of detecting, when rapid catalyst warm-up is necessary, the temperature of the engine coolant THW, the step of estimating, when the THW is lower than a predetermined threshold value, the amount of fuel sticking to the wall surface of an intake port and calculating a cold-state increase correction value Q (P) for an intake manifold injector, the step of changing the DI ratio r to satisfy the cold-state increase correction value Q (P), and the step of performing the rapid catalyst warm-up.

This nonprovisional application is based on Japanese Patent Application No. 2005-078285 filed with the Japan Patent Office on Mar. 18, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control apparatus for an internal combustion engine including a first fuel injection mechanism (in-cylinder injector) for injecting fuel into a cylinder and a second fuel injection mechanism (intake manifold injector) for injecting fuel into an intake manifold or intake port. In particular, the invention relates to a control apparatus for an internal combustion engine for use in the case where a catalyst for cleaning exhaust gases is rapidly warmed up.

2. Description of the Background Art

An internal combustion engine is well-known that includes an intake manifold injector for injecting fuel into an engine intake manifold and an in-cylinder injector for injecting fuel into an engine combustion chamber, for which the ratio of fuel injection between the intake manifold injector and the in-cylinder injector is determined based on an engine speed and an engine load.

Japanese Patent Laying-Open No. 11-324765 discloses a control apparatus for a direct-injection spark-ignition internal combustion engine that activates, at an early stage after engine start, a catalyst for cleaning exhaust gases. This control apparatus for the direct-injection spark-ignition internal combustion engine includes a fuel injection valve for injecting and supplying fuel directly into a combustion chamber of the engine, fuel supply means for creating a homogeneous air-fuel mixture in the entire combustion chamber, and a spark plug for producing a spark to ignite the air-fuel mixture within the combustion chamber. The direct-injection spark-ignition internal combustion engine is controlled in such a manner that the quantity of injected fuel and the fuel injection timing of the fuel injection valve in a compression stroke as well as the ignition timing of the spark plug are controlled such that the air-fuel ratio of an air-fuel mixture layer locally located around the spark plug when the mixture is ignited is stoichiometric under a predetermined engine operating condition, and accordingly stratified charge combustion is performed. The control apparatus further includes temperature-increase condition determination means for making a determination as to the condition under which an exhaust cleaning catalyst provided in an exhaust manifold of the engine should be increased in temperature as well as control means for controlling, under the condition where the exhaust cleaning catalyst should be increased in temperature, the quantity of fuel injected by the fuel supply means so as to allow the air-fuel ratio of the air-fuel mixture generated in the whole combustion chamber to be lean rather than stoichiometric and to be an air-fuel ratio at which flame can be propagated, and controlling the quantity of injected fuel and the fuel injection timing of the fuel injection valve in a compression stroke and the ignition timing of the spark plug so as to allow the air-fuel ratio of the air-fuel mixture locally located around the spark plug when the mixture is ignited to be rich rather than stoichiometric, thereby achieving a second stratified charge combustion.

Regarding this control apparatus for the direct-injection spark-ignition internal combustion engine, the air-fuel ratio of the air-fuel mixture layer around the spark plug is set to be rich rather than stoichiometric, and thus an incomplete combustion product (CO) is generated in a main combustion process (ignition by spark and subsequent combustion through flame propagation) and this CO remains in the combustion chamber after the main combustion. Further, since the air-fuel mixture generated around the rich air-fuel mixture is lean rather than stoichiometric, oxygen remains in this region after the main combustion. Flow of gases in the cylinder after the main combustion causes the remaining CO and the remaining oxygen to be mixed and re-burned, resulting in an increase in exhaust temperature. Since the incomplete combustion product (CO) is generated in the process of main combustion, the incomplete combustion product has already been in a high-temperature state when the main combustion is completed. Therefore, the CO can be burned in a relatively favorable state even under the condition where the combustion-chamber temperature is low. In other words, almost all of the generated CO can be re-burned in the combustion chamber and in the exhaust manifold upstream of the catalyst. Although an increased quantity of CO could flow to the catalyst as compared with homogeneous charge combustion which generates a smaller quantity of CO in the main combustion itself, the catalyst starts CO conversion at a temperature lower than the HC conversion starting temperature and thus exhaust emissions are influenced to a relatively small degree. Further, since the air-fuel ratio of the lean air-fuel mixture layer is set to an air-fuel ratio at which flame can be propagated, un-burned HC is not generated at the boundary between the rich air-fuel mixture layer and the lean air-fuel mixture layer. Furthermore, since the flame is propagated to every corner of the combustion chamber in a favorable state, the low-temperature region (quench area) in the combustion chamber may be a small region which is the same as the one for the homogeneous charge combustion. Moreover, since an excessive quantity of oxygen in a region where the lean air-fuel mixture is burned is left after the main combustion, the temperature of the remaining oxygen when the main combustion is completed is relatively high, so that CO is more quickly re-burned.

Japanese Patent Laying-Open No. 11-324765 discussed above includes a fourth embodiment showing the following structure. Fuel supply means for creating a homogeneous air-fuel mixture in the entire combustion chamber is provided to generate a homogeneous air-fuel mixture that is relatively lean rather than stoichiometric in the whole combustion chamber through fuel injection by means of a fuel injection valve (fuel injection valve for intake port injection) provided in the intake manifold in an exhaust stroke or in a period from an exhaust stroke to an intake stroke. A fuel injection valve for injecting fuel into the cylinder is used to inject and supply fuel into the combustion chamber in a compression stroke and create an air-fuel mixture in a layered form that is relatively rich (high fuel concentration) rather than stoichiometric around the spark plug, and the mixture is burned. For a stratified stoichiometric charge combustion with the purpose of activating a catalyst, fuel is supplied in the following way. Specifically, of the total quantity of fuel that can be almost completely burned with a quantity of intake air per combustion cycle (weight of fuel necessary for achieving a substantially stoichiometric ratio), from approximately 50% to approximately 90% for example of the weight of fuel is injected and supplied into the intake manifold by means of the fuel injection valve for intake port injection (in an exhaust stroke or from exhaust stroke to intake stroke), thereby generating a homogeneous air-fuel mixture that is relatively lean rather than stoichiometric in the entire combustion chamber in an intake stroke. Further, from approximately 50% to approximately 10% of the remaining weight of fuel is injected and supplied into the combustion chamber by means of the fuel injection valve for injecting fuel into the cylinder in a compression stroke, and an air-fuel mixture that is relatively rich (high fuel concentration) rather than stoichiometric around the spark plug is generated in a layered form, and the mixture is burned. In other words, when the catalyst is heated, regarding the fuel injection ratio between the in-cylinder fuel injection valve and the intake manifold fuel injection valve, at least the fuel injection ratio of the intake manifold fuel injection valve is higher.

However, in order to achieve early warm-up of the exhaust catalyst, the aforementioned fuel injection ratio is not optimum for the internal combustion engine having the fuel injection valve for injecting fuel into the cylinder (in-cylinder injector) and the fuel injection valve for injecting fuel into the intake manifold (intake manifold injector). In other words, as to the ignition timing that is the most important factor for catalyst warm-up, a sufficient retard cannot be achieved at such a fuel injection ratio.

Further, when the engine is in a cold state and in the range where the in-cylinder injector and the intake manifold injector partake in the fuel injection, a difference between the degree to which the temperature increases in the cylinder and the degree to which the temperature of the intake port increases results in a difference of the degree to which the injected fuel sticks to the wall surface and the degree to which the injected fuel sticks to the piston top surface. Therefore, the amount of fuel sticking to the wall surface has to be taken into consideration to determine the fuel injection ratio. Otherwise, the target fuel injection ratio and the fuel injection ratio in the combustion chamber do not agree with each other, so that the above-described combustion manner cannot be obtained and thus the early warm-up of the catalyst cannot be achieved. In such a case, the fuel is increased by the quantity corresponding to the amount of fuel sticking to the wall surface of the intake port that is lower in temperature. However, if the quantity of fuel to be injected from the intake manifold injector is merely increased, the total quantity of fuel increases, resulting in deterioration in fuel economy or deterioration in components of the exhaust.

Furthermore, in the cold state, although a correction for increase is made that corresponds to the amount of fuel sticking to the wall surface of the intake port, the fuel increased by this increase correction has to be decreased when the influence of the temperature disappears. However, depending on the degree to which the fuel is decreased (attenuation ratio), the target fuel injection ratio as described above and the fuel injection ratio in the combustion chamber do not agree with each other. Then, the early catalyst warm-up cannot be achieved.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a control apparatus for an internal combustion engine having a first fuel injection mechanism for injecting fuel into a cylinder and a second fuel injection mechanism for injecting fuel into an intake manifold, performing, in a favorable manner, rapid warm-up of an exhaust cleaning catalyst at the start of the internal combustion engine while causing no increase in total fuel quantity by considering fuel sticking to the wall surface in a cold state.

A control apparatus according to the present invention controls an internal combustion engine that includes a first fuel injection mechanism injecting fuel into a cylinder, a second fuel injection mechanism injecting fuel into an intake manifold, and an ignition device. The internal combustion engine has an exhaust system provided with a catalyst that is used for cleaning exhaust and that is activated at a temperature of at least a predetermined temperature. The control apparatus includes: a detection unit detecting a request to warm up the catalyst; a control unit controlling the first and second fuel injection mechanisms, based on conditions required of the internal combustion engine, such that the first and second fuel injection mechanisms partake in fuel injection; an ignition control unit controlling the ignition device; and a temperature detector detecting the temperature of the internal combustion engine. The control unit controls the first and second fuel injection mechanisms, considering the temperature of the internal combustion engine, such that the ratio of fuel injection by the first fuel injection mechanism is at least equal to the ratio of fuel injection by the second fuel injection mechanism under the conditions that the first and second fuel injection mechanisms partake in the fuel injection and the request to warm up is detected. The ignition control unit controls the ignition device to retard ignition timing when the request to warm up is detected.

In accordance with the present invention, the ratio of fuel injection by the first fuel injection mechanism (in-cylinder injector for example) is set to be equal to or higher than the ratio of fuel injection by the second fuel injection mechanism (intake manifold injector for example) (the in-cylinder injector performs 65% of the fuel injection for example), and fuel is injected by means of the in-cylinder injector in a compression stroke. Accordingly, in the combustion chamber, a homogeneous air-fuel mixture (air-fuel mixture at a lean air-fuel ratio as a whole) generated by the intake manifold injector as well as a stratified air-fuel mixture (air-fuel mixture at a rich air-fuel ratio around the spark plug) generated by the in-cylinder injector can be created. At this time, in particular, the fuel injection ratio of the in-cylinder injector is equal to or higher than that of the intake manifold injector, and thus the air-fuel ratio of the air-fuel mixture around the spark plug can be made richer. Further, since the air-fuel mixture around the rich mixture is the homogeneous air-fuel mixture, flame can be propagated in a favorable state. In other words, in the state where fuel is sprayed, even at the boundary between the air-fuel mixture layer with the rich air-fuel ratio around the spark plug and the homogeneous air-fuel mixture, any region where the air-fuel ratio becomes lean due to diffusion of the fuel does not partially occur. Since such a region is not generated, flame is easily propagated and unburned fuel (HC) is unlikely to be generated. In such a state, the ignition timing can be retarded to a large degree and the exhaust temperature can easily be increased. It is considered that the exhaust temperature is increased for the following reason. The air-fuel ratio of the air-fuel mixture around the spark plug is rich rather than stoichiometric, so that an incomplete combustion product (CO) is generated in a main combustion process (ignition by spark generated by the spark plug and subsequent combustion through propagation of flame) and this CO remains in the combustion chamber after the main combustion. In the homogeneous air-fuel mixture with the lean air-fuel ratio located around the air-fuel mixture at the rich air-fuel ratio, oxygen remains after the main combustion. The remaining CO and the remaining oxygen are mixed through gas flow in the cylinder and then burned again, causing the exhaust temperature to increase. Since the exhaust temperature increases, in the period from the engine start to activation of the catalyst, emission of HC into the atmosphere can be suppressed. Meanwhile, the catalyst can rapidly be warmed up to be activated at an early stage. When the engine is started in a cold state in which the temperature of the internal combustion engine is low, such a warm-up operation as described above is performed. At this time, the in-cylinder injector injects fuel directly into the high-temperature cylinder, and thus atomization is in a favorable state. In contrast, since the intake manifold injector injects fuel into the low-temperature intake port, atomization is not in a favorable state. In other words, some fuel sticks to the wall surface of the intake port, resulting in poor atomization. In such a case, usually, to the quantity of fuel to be injected from the intake manifold injector, the amount of fuel sticking to the wall surface is added to inject the fuel into the intake port (increase correction). Therefore, the total fuel quantity (the sum of the quantity of fuel injected from the in-cylinder injector and the quantity of fuel injected from the intake manifold injector to which the amount of fuel sticking to the wall surface is added) increases to cause deterioration in fuel economy and exhaust components. According to the present invention, when the temperature of the internal combustion engine is lower, the ratio of fuel injection by the in-cylinder injector is lowered while the ratio of fuel injection by the intake manifold injector is increased to increase the quantity of fuel injected by the intake manifold injector. In this way, the fuel is injected in consideration of the fuel sticking to the wall surface. Since only the ratio of fuel injection is changed while the total fuel quantity remains the same, deterioration in fuel economy and exhaust components can be avoided. In this way, there can be provided a control apparatus for an internal combustion engine having a first fuel injection mechanism injecting fuel into a cylinder and a second fuel injection mechanism injecting fuel into an intake manifold, performing rapid warm-up of an exhaust cleaning catalyst at engine start in a favorable manner to cause no increase in total fuel quantity in consideration of the fuel sticking to the wall surface in a cold state.

Preferably, the control apparatus further includes a calculation unit calculating, based on the temperature of the internal combustion engine, an amount of wall-sticking fuel that is an amount of fuel injected by the second fuel injection mechanism into the intake manifold and sticking to a wall surface. The control unit controls, considering the amount of wall-sticking fuel, the first and second fuel injection mechanisms.

In accordance with the present invention, the calculation unit calculates the amount of fuel sticking to the wall surface based on the temperature of the internal combustion engine. With this amount of fuel sticking to the wall surface taken into account, the ratio of fuel injection by the in-cylinder injector is lowered while that of the intake manifold injector is increased to increase the quantity of fuel injected from the intake manifold injector by the quantity corresponding to the amount of fuel sticking to the wall surface, without increase in total fuel quantity.

Still preferably, the control unit changes, considering the amount of wall-sticking fuel, the ratio of fuel injection between the first fuel injection mechanism and the second fuel injection mechanism by increasing the ratio of fuel injection by the second fuel injection mechanism.

In accordance with the present invention, the amount of fuel sticking to the wall surface is taken into account and the ratio of fuel injection by the in-cylinder injector is lowered while that of the intake manifold injector is increased. Thus, the quantity of fuel injected from the intake manifold injector can be increased by the quantity corresponding to the amount of fuel sticking to the wall surface, without increasing the total fuel quantity.

Still preferably, the control unit changes the ratio of fuel injection between the first fuel injection mechanism and the second fuel injection mechanism by making an increase correction to the quantity of injected fuel injected by the second fuel injection mechanism according to the amount of wall-sticking fuel and increasing the ratio of fuel injection by the second fuel injection mechanism.

In accordance with the present invention, the ratio of fuel injection by the intake manifold injector is increased for an increase by the amount of fuel sticking to the wall surface (the ratio of fuel injection by the in-cylinder injector is relatively decreased). Thus, without increase in total fuel quantity, the amount of fuel injected from the intake manifold injector can be increased by the quantity corresponding to the amount of fuel sticking to the wall surface.

Still preferably, the control unit controls the first and second fuel injection mechanisms such that the sum of the quantity of injected fuel injected by the first fuel injection mechanism and the quantity of injected fuel injected by the second fuel injection mechanism in the case where the amount of wall-sticking fuel is considered is smaller than that in the case where the amount-of wall-sticking fuel is not considered.

In accordance with the present invention, the amount of fuel sticking to the wall surface is considered to decrease the ratio of fuel injection by the in-cylinder injector and increase the ratio of fuel injection by the intake manifold injector. Thus, by the quantity corresponding to the amount of fuel sticking to the wall surface, the amount of fuel injected from the intake manifold injector can be increased, while the total fuel quantity is not increased.

Still preferably, the control apparatus further includes a decrease unit attenuating, based on the temperature of the internal combustion engine, the quantity of injected fuel which is injected by the second fuel injection mechanism and to which the increase correction is made.

In accordance with the present invention, it is necessary to return to the original state the quantity of fuel corresponding to the increase correction that is injected by the intake manifold injector, as the temperature of the internal combustion engine increases. At this time, depending on the temperature of the internal combustion engine, the attenuation ratio of the increase correction (for example, the degree to which the decrease is made per unit time) is determined. Then, while maintaining the ratio appropriate for rapidly warming up the catalyst, the fuel quantity corresponding to the increase correction can be returned to the original state.

Still preferably, the decrease unit more sharply attenuates the quantity of injected fuel to which the increase correction is made, as the temperature of the internal combustion engine is higher.

In accordance with the present invention, as the temperature of the internal combustion engine is higher (or as the degree to which the internal combustion engine increases in temperature is larger), the degree to which the amount of fuel sticking to the wall surface of the intake port has to be considered decreases. Therefore, as the temperature of the internal combustion engine is higher, the quantity of injected fuel corresponding to the increase correction can more sharply be attenuated to return to the original state.

Still preferably, the decrease unit more slowly attenuates the quantity of injected fuel to which the increase correction is made, as the temperature of the internal combustion engine is lower.

In accordance with the present invention, as the temperature of the internal combustion engine is lower (or the degree to which the internal combustion engine increases in temperature is smaller), a longer time is required for which it is highly necessary to consider the amount of fuel sticking to the wall surface of the intake port. Therefore, as the temperature of the internal combustion engine is lower, the quantity of fuel corresponding to the increase correction is more slowly attenuated to return to the original state. Thus, a desired combustion state is achieved and the catalyst can rapidly be warmed up.

Still preferably, the decrease unit decreases, from the quantity of injected fuel injected by the second fuel injection mechanism, the quantity of fuel corresponding to the increase correction.

In accordance with the present invention, from only the intake manifold injector to which the increase correction is made, the decrease is made for returning to the original state.

Still preferably, the decrease unit decreases, from the quantity of injected fuel injected by the first fuel injection mechanism and from the quantity of injected fuel injected by the second fuel injection mechanism, the quantity of fuel corresponding to the increase correction.

In accordance with the present invention, from both of the intake manifold injector to which the increase correction is made and the in-cylinder injector, the quantity of fuel can be decreased in consideration of the fuel injection ratio.

Still preferably, the decrease unit decreases the quantity of fuel corresponding to the increase correction, such that the ratio of fuel injection between the first fuel injection mechanism and the second fuel injection mechanism before the increase correction is made is maintained.

In accordance with the present invention, the decrease is made from both of the intake manifold injector to which the increase correction is made as well as the in-cylinder injector for returning to the original state, while maintaining the fuel injection ratio before the increase correction is made.

Still preferably, the decrease unit decreases the quantity of fuel corresponding to the increase correction, such that the ratio of fuel injection between the first fuel injection mechanism and the second fuel injection mechanism after the increase correction is made is maintained.

In accordance with the present invention, the decrease is made from both of the intake manifold injector to which the increase correction is made as well as the in-cylinder injector for returning to the original state, while maintaining the fuel injection ratio after the increase correction is made.

Still preferably, the first fuel injection mechanism is an in-cylinder injector and the second fuel injection mechanism is an intake manifold injector.

In accordance with the present invention, for the internal combustion engine separately including the in-cylinder injector that is the first fuel injection mechanism and the intake manifold injector that is the second fuel injection mechanism to allow fuel injection to be performed by both injectors, a control apparatus can be provided to perform rapid warm-up of the exhaust cleaning catalyst at the start of the internal combustion engine to cause no increase in total fuel quantity, considering the amount of fuel sticking to the wall surface in the cold state.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a structure of an engine system controlled by a control apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a control structure of a program executed by an engine ECU identified as the control apparatus of the embodiment of the present invention.

FIG. 3 shows conditions for rapid catalyst warm-up in the embodiment of the present invention.

FIG. 4 shows a state in which the engine ECU identified as the control apparatus of the embodiment of the present invention makes an increase for addressing fuel sticking to the wall surface.

FIGS. 5 to 7 each show a state in which the engine ECU identified as the control apparatus of the embodiment of the present invention makes a decrease of the increase for addressing fuel sticking to the wall surface.

FIG. 8 represents a DI ratio map corresponding to a warm state of an engine (1) to which the control apparatus of the embodiment of the present invention is suitably applied.

FIG. 9 represents a DI ratio map corresponding to a cold state of the engine (1) to which the control apparatus of the embodiment of the present invention is suitably applied.

FIG. 10 represents a DI ratio map corresponding to a warm state of an engine (2) to which the control apparatus of the embodiment of the present invention is suitably applied.

FIG. 11 represents a DI ratio map corresponding to a cold state of the engine (2) to which the control apparatus of the embodiment of the present invention is suitably applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are hereinafter described with reference to the drawings. In the following description, like components are denoted by like reference characters, and these components are named identically and function identically. Therefore, a detailed description thereof is not repeated.

FIG. 1 is a schematic of a structure of an engine system controlled by an engine ECU (Electronic Control Unit) identified as a control apparatus for an internal combustion engine according to an embodiment of the present invention. Although an in-line 4-cylinder gasoline engine is shown in FIG. 1 as the engine, the present invention is not limited to such an engine.

As shown in FIG. 1, engine 10 includes four cylinders 112, each connected to a common surge tank 30 via a corresponding intake manifold 20. Surge tank 30 is connected via an intake duct 40 to an air cleaner 50. In intake duct 40, an airflow meter 42 is placed and a throttle valve 70 driven by an electric motor 60 is also placed. Throttle valve 70 has its degree of opening controlled based on an output signal of an engine ECU 300, independently of an accelerator pedal 100. Each cylinder 112 is connected to a common exhaust manifold 80, which is in turn connected to a three-way catalytic converter 90.

For each cylinder 112, an in-cylinder injector 110 for injecting fuel into the cylinder and an intake manifold injector 120 for injecting fuel into an intake port or/and an intake manifold are provided. Injectors 110 and 120 are controlled based on output signals from engine ECU 300. Further, each in-cylinder injector 110 is connected to a common fuel delivery pipe 130. Fuel delivery pipe 130 is connected to a high-pressure fuel pump 150 of an engine-driven type, via a check valve 140 that allows a flow in the direction toward fuel delivery pipe 130. Although an internal combustion engine having two injectors separately provided is explained in connection with the present embodiment, the present invention is not restricted to such an internal combustion engine. For example, the internal combustion engine may have one injector that can effect both in-cylinder injection and intake manifold injection.

As shown in FIG. 1, the discharge side of high-pressure fuel pump 150 is connected via an electromagnetic spill valve 152 to the intake side of high-pressure fuel pump 150. As the degree of opening of electromagnetic spill valve 152 is smaller, the quantity of fuel supplied from high-pressure fuel pump 150 into fuel delivery pipe 130 increases. When electromagnetic spill valve 152 is fully opened, the fuel supply from high-pressure fuel pump 150 to fuel delivery pipe 130 is ceased. Electromagnetic spill valve 152 is controlled based on an output signal of engine ECU 300.

Each intake manifold injector 120 is connected to a common fuel delivery pipe 160 at the low-pressure side. Fuel delivery pipe 160 and high-pressure fuel pump 150 are connected to an electromotor-driven-type low-pressure fuel pump 180 via a common fuel pressure regulator 170. Low-pressure fuel pump 180 is connected to a fuel tank 200 via a fuel filter 190. When the fuel pressure of fuel ejected from low-pressure fuel pump 180 becomes higher than a predetermined set fuel pressure, fuel pressure regulator 170 returns a portion of the fuel ejected from low-pressure fuel pump 180 to fuel tank 200. Accordingly, the fuel pressure supplied to intake manifold injector 120 and the fuel pressure supplied to high-pressure fuel pump 150 are prevented from becoming higher than the set fuel pressure.

Engine ECU 300 is configured with a digital computer, and includes a ROM (Read-Only Memory) 320, a RAM (Random Access Memory) 330, a CPU (Central Processing Unit) 340, an input port 350, and an output port 360 connected to each other via a bidirectional bus 310.

Airflow meter 42 generates an output voltage in proportion to the quantity of intake air. The output voltage of airflow meter 42 is applied to input port 350 via an A/D converter 370. A coolant temperature sensor 380 generating an output voltage in proportion to the engine coolant temperature is attached to engine 10. The output voltage of coolant temperature sensor 380 is applied to input port 350 via an A/D converter 390.

A fuel pressure sensor 400 generating an output voltage in proportion to the fuel pressure in fuel delivery pipe 130 is attached to fuel delivery pipe 130. The output voltage of fuel pressure sensor 400 is applied to input port 350 via an A/D converter 410. An air-fuel ratio sensor 420 generating an output voltage in proportion to the oxygen concentration in the exhaust gas is attached to exhaust manifold 80 upstream of 3-way catalytic converter 90. The output voltage of air-fuel ratio sensor 420 is applied to input port 350 via an A/D converter 430.

Air-fuel ratio sensor 420 in the engine system of the present embodiment is a full-range air-fuel ratio sensor (linear air-fuel ratio sensor) generating an output voltage in proportion to the air-fuel ratio of an air-fuel mixture burned in engine 10. Air-fuel ratio sensor 420 may be an O₂ sensor that detects whether the air-fuel ratio of the air-fuel mixture burned in engine 10 is rich or lean with respect to the stoichiometric ratio in an on/off manner.

Accelerator pedal 100 is connected to an accelerator pedal position sensor 440 generating an output voltage in proportion to the pedal position of accelerator pedal 100. The output voltage of accelerator pedal position sensor 440 is applied to input port 350 via an A/D converter 450. To input port 350, an engine speed sensor 460 generating an output pulse representing the engine speed is connected. ROM 320 of engine ECU 300 stores the value of the fuel injection quantity set corresponding to an operation state, a correction value based on the engine coolant temperature, and the like that are mapped in advance based on the engine load factor and the engine speed obtained through accelerator pedal position sensor 440 and engine speed sensor 460 set forth above.

Three-way catalytic converter 90 can oxidize CO and HC and reduce NOx in exhaust gases when the air-fuel ratio is near the stoichiometric air-fuel ratio (A/F (air weight/fuel weight)=14.7), thereby cleaning the exhaust gases. The catalyst (platinum, rhodium, paradigm for example) of this three-way catalytic converter 90 is not activated and thus does not exhibit the cleaning ability until reaching a certain (high) temperature.

The control apparatus of the present embodiment increases the temperature of three-way catalytic converter 90 at an early stage to activate the catalyst, after engine 10 having in-cylinder injector 110 and intake manifold injector 120 is started, thereby effecting cleaning of exhaust gases as early as possible immediately after engine 10 is started. The control apparatus limit such an early temperature-increasing operation in the case where the vehicle having this engine 10 mounted thereon has a great height. Whether or not three-way catalytic converter 90 is activated can be determined by detecting the concentration of a specific component (for example oxygen) in exhaust gases at the downstream of the exhaust gases of three-way catalytic converter 90. For example, it is determined whether or not an oxygen sensor provided downstream of three-way catalytic converter 90 is activated. Specifically, whether or not three-way catalytic converter 90 is activated is determined based on a change in detection signal of the downstream oxygen sensor. Since the activation of the oxygen sensor provided downstream of three-way catalytic converter 90 is caused by an increase in temperature of exhaust gases (oxidation) on the outlet side of activation of three-way catalytic converter 90, it is determined that-three-way catalytic converter 90 is activated based on the fact that the oxygen sensor is activated.

Alternatively, the temperature of the engine coolant or the temperature of the engine oil for example may be detected to estimate the temperature of three-way catalytic converter 90 and accordingly determine whether or not three-way catalytic converter 90 is activated based on the result of the estimation. Further, the temperature of three-way catalytic converter 90 (outlet temperature) may directly be detected to determine whether or not three-way catalytic converter 90 is activated.

When the temperature of engine 10 (the temperature determined from the value detected by coolant temperature sensor 380 that detects the engine coolant) is low, the intake manifold is also low in temperature. Therefore, the fuel injected from intake manifold injector 120 sticks to the wall surface of the low-temperature intake port so that the state of atomization of the fuel is unfavorable. Accordingly, in usual, a correction for increase or increase correction is made by increasing the fuel to be injected from intake manifold injector 120 by the quantity corresponding to the amount of fuel sticking to the wall surface. This increase correction causes an increase of the total fuel quantity (the sum of the quantity of fuel injected from in-cylinder injector 110 and the quantity of fuel that is injected from intake manifold injector 120 and that is increased by the quantity corresponding to the amount of fuel sticking to the wall surface) and thus deteriorates fuel economy and components of the exhaust. A program executed by engine ECU 300 identified as the control apparatus of the present embodiment is used to achieve early catalyst warm-up without increase in total fuel quantity.

In this engine 10, in-cylinder injector 110 and intake manifold injector 120 partake in or share the injection of fuel. A description is now given of a map that is stored in ROM 320 of engine ECU 300 and that represents the fuel injection ratio between in-cylinder injector 110 and intake manifold injector 120 (hereinafter also referred to as direct injection ratio, DI ratio, DI ratio r (or simply r)). This map has its horizontal axis representing the engine speed and its vertical axis representing the load factor to indicate, as the direct injection ratio (DI ratio r), the ratio of fuel injection by in-cylinder injector 110 expressed in percentage.

For each of operating regions determined by the engine speed and load factor, a direct-injection ratio (DI ratio r) is set. “Direct injection 100%” means that the region is a region where fuel is injected from in-cylinder injector 110 only (r=1.0, r=100%). “Direct injection 0-20%” means that the region is a region where 0 to 20% of the total quantity of injected fuel is injected from in-cylinder injector 110 (r=0-0.2). For example, “direct injection 40%” means that 40% of the total quantity of injected fuel is injected from in-cylinder injector 120 while the remaining 60% of the total quantity of injected fuel is injected from intake manifold injector 120. Details of this map are given hereinlater.

Referring to FIG. 2, a control structure of a program is described that is executed by engine ECU 300 identified as the control apparatus in the embodiment of the present invention.

In step (hereinafter “step” is abbreviated as “S”) 100, engine ECU 300 determines whether or not engine 10 is started. At this time, the determination is made based on an engine start request signal that is input to engine ECU 300 from another ECU and/or the results of processing by engine ECU 300 itself. As engine 10 is started (YES in S1OO), the process proceeds to S110. If not (NO in S1OO), this process is ended.

In S110, engine ECU 300 determines whether or not rapid catalyst warm-up is necessary. At this time, as described above, if it is found, from a change in the detection signal of the oxygen sensor provided downstream of three-way catalytic converter 90, that three-way catalytic converter 90 is not activated, it is determined that the rapid catalyst warm-up is necessary. Alternatively, from the temperature of the engine coolant or the temperature of the engine oil, it may be determined whether or not the rapid catalyst warm-up is necessary. When the rapid catalyst warm-up is necessary (YES in S110), the process proceeds to S120. If not (NO in S110), the process proceeds to S190.

In S120, engine ECU 300 detects the coolant temperature THW of this engine 10. At this time, the engine coolant temperature THW is detected based on a signal from coolant sensor 380.

In S130, engine ECU 300 determines whether or not the coolant temperature THW is lower than a threshold value THW (1). When it is determined that the coolant temperature THW is lower than the threshold value THW (1) (YES in S130), the process proceeds to S140. If not (NO in S130), the process proceeds to S170. In the case where it is determined that the coolant temperature THW is equal to or lower than the threshold value THW (1), the process may proceed to S140.

In S140, engine ECU 300 estimates the amount of fuel sticking to the wall surface of the port. At this time, engine ECU 300 may estimate, from such factors as the coolant temperature THW of engine 10 and the temperature of the outside air (temperature of intake air), the amount of fuel sticking to the port wall surface using a predetermined map.

In S150, engine ECU 300 calculates a correction value for increase in a cold state, namely a cold-state increase correction value Q (P) for intake manifold injector 120. This cold-state increase correction value Q (P) corresponds to a quantity of fuel for an increase corresponding to the amount of fuel sticking to the wall surface of the port.

In S160, engine ECU 300 changes the DI ratio r such that the quantity of fuel determined by adding the cold-state increase correction value Q (P) to a basic fuel quantity of intake manifold injector 120 is the quantity of fuel to be injected from intake manifold injector 120. At this time, the total fuel quantity (the sum of the quantity of fuel from in-cylinder injector 110 and the quantity of fuel that is injected from intake manifold injector 120 and that is increased by the amount corresponding to the amount of fuel sticking to the port wall surface) does not increase. The details for this will be given hereinlater.

In S170, engine ECU 300 performs an operation for the rapid catalyst warm-up. At this time, for example, as shown in FIG. 3, engine ECU 300 controls the ignition timing, the injection timing by in-cylinder injector 110, the quantity of injected fuel, the quantity of supplied air, and the DI ratio r. The numerical values of the DI ratio indicated in FIG. 3 are exemplary ones and the DI ratio may be at least 50% (the ratio of fuel injection by in-cylinder injector 110 is equivalent to or higher than the ratio of fuel injection by intake manifold injector 120). Further, regarding the decrease in fuel quantity, the air-fuel ratio of exhaust gases may be for example approximately 15.5 corresponding to a lean state. By this decrease, unburned HC is also decreased. While a correction for increase is made immediately after engine 10 is started (an increase correction for addressing a request for torque when engine 10 is started or an increase correction for addressing sticking of fuel to the wall surface), the fuel quantity is decreased since the torque requested at the engine start becomes unnecessary after certain time has passed since the engine start or the fuel sticking to the wall surface is saturated. Thus, even if the quantity of fuel injected in a compression stroke from in-cylinder injector 110 is decreased, only the quantity of fuel necessary for ignition is present around the spark plug and a high lean limit is kept so that no misfire occurs. Fuel for post combustion of a requested quantity that contributes to catalyst warm-up (fuel supplied from intake manifold injector 120) is supplied (by the increase correction). The supplied post-combustion fuel can be used to warm up the catalyst.

In S180, engine ECU 300 determines whether or not the rapid catalyst warm-up should be ended. At this time, as described above, if it is found, from a change in detection signal of the oxygen sensor provided downstream of three-way catalyst converter 90, that three-way catalyst converter 90 is activated, it is determined that the rapid catalyst warm-up is to be ended. Alternatively, from the temperature of the engine coolant or the temperature of the engine oil for example, the determination as to whether or not the rapid catalyst warm-up should be ended may be made. Further, alternatively, depending on whether or not the temperature of the engine coolant has reached a predetermined temperature or higher relative to the temperature at the engine start, it may be determined whether or not the rapid catalyst warm-up should be ended. Furthermore, alternatively, based on the total quantity of intake air, the determination as to whether or not engine 10 has been operating for a predetermined time or more may be made to determine whether or not the rapid catalyst warm-up should be ended. When it is determined that the rapid catalyst warm-up is to be ended (YES in S180), the process proceeds to S190. If not (NO in S180), the process returns to S170 to continue the rapid catalyst warm-up.

In S190, engine ECU 300 performs a normal operation for engine 10. At this time, the ignition timing, the injection timing of in-cylinder injector 110, the quantity of injected fuel, the quantity of supplied air and the DI ratio r that are temporarily set for the rapid catalyst warm-up are set back to those for the normal operation by engine ECU 300.

A description is now given of an operation of engine 10 controlled by engine ECU 300 identified as the control apparatus of the present embodiment, based on the above-described structure and flowchart. In the following, the description is given of the operation at start-up of engine 10 in the case where rapid catalyst warm-up is necessary and a correction is made for an increase, in a cold state, to the quantity of fuel injected from intake manifold injector 120.

Under the conditions that engine 10 is started (YES in S100) and it is found from a change in the detection signal of the oxygen sensor provided downstream of three-way catalytic converter 90 that three-way catalytic converter 90 is not activated, it is determined that the rapid catalyst warm-up is necessary (YES in S110). The temperature of engine 10 (coolant temperature THW) is detected (S120). When the coolant temperature THW is lower than the threshold value THW (1), the amount of fuel that is included in the fuel injected from intake manifold injector 120 and that sticks to the wall surface of the port is estimated (S140). From this estimated amount of fuel sticking to the wall surface, the cold-state increase correction value Q (P) for intake manifold injector 120 is calculated (S150). Then, the fuel injection ratio between in-cylinder 110 and intake manifold injector 120 is changed such that an increase corresponding to this cold-state increase correction value Q (P) is made.

The state at this time is described in connection with FIG. 4. For the sake of simplicity in description, it is supposed here that basic conditions for the catalyst warm-up calculated based on FIG. 3 are that the total fuel quantity is 1.00 and the DI ratio r is 65% (in the case where the correction for addressing the fuel sticking to the port wall surface in a cold state is not considered). This state of fuel injection is shown at (A) in FIG. 4. Since the total fuel quantity is 1.00, the fuel injection quantity Q (D) ALL from in-cylinder injector 110 is 0.65 while the fuel injection quantity Q (P) ALL from intake manifold injector 120 is 0.35. It is further supposed that the amount of fuel sticking to the wall surface that is estimated at this time is 0.20 and the cold-state increase correction value Q (P) is also 0.20 (actually, cold-state increase correction value Q (P) is calculated from the estimated amount of fuel sticking to the wall surface in consideration of other factors). In other words, as indicated at (B) in FIG. 4, the quantity of fuel Q (P) ALL of 0.35 injected from intake manifold injector 120 includes the quantity of fuel 0.20 that sticks to the wall surface and thus that is not used for combustion. Therefore, of the total quantity of fuel 1.00, the quantity of fuel contributing to combustion is the sum of the quantity 0.65 of fuel injected from in-cylinder injector 110 and the quantity 0.15 (included in 0.35) of fuel injected from intake manifold injector 120, namely 0.80.

In such a case, in a conventional example as indicated at (D) in FIG. 4, the cold-state increase correction value Q (P) of 0.20 is added to only the quantity of fuel injected from intake manifold injector 120. At this time, the total fuel quantity is 1.20. In another conventional example as indicated at (E) in FIG. 4, the cold-state increase correction value Q (P) of 0.20 is added to each of the quantity of fuel injected from the in-cylinder injector and the quantity of fuel injected from the intake manifold injector. At this time, the total fuel quantity is 1.40. In still another conventional example as indicated at (F) in FIG. 4, the quantity of fuel injected from in-cylinder injector 110 is increased such that the DI ratio r indicated at (A) in FIG. 4 (=65%) remains the same even after the cold-state increase correction value Q (P) of 0.2 is added to only the quantity of fuel injected from intake-manifold injector 120. In this case, the total fuel quantity is 1.57.

In contrast, engine ECU 300 identified as the control apparatus of the present embodiment changes the DI ratio r as indicated at (C) in FIG. 4 (S160). More specifically, the DI ratio r is decreased from 65% to 56% to allow intake manifold injector 120 to inject the quantity of fuel including the cold-state increase correction value Q (P). In this case, the total fuel quantity is 0.80.

At this DI ratio r (=56%) changed as described above, the rapid catalyst warm-up is carried out (S170). Conditions except for this DI ratio r at this time are those as shown in FIG. 3.

In the engine controlled in such a manner as described above, the ratio of fuel injection by in-cylinder injector 110 is set to be equivalent to that by intake manifold injector 120 or to be higher than that, approximately 65% (56% in this case), to inject fuel into the cylinder in a compression stroke from in-cylinder injector 110. From intake manifold injector 120, fuel is injected into the intake manifold in an intake stroke. At this time, an air-fuel mixture that is produced by intake-manifold injector 120, entirely lean in air-fuel ratio and in a homogeneous state as well an air-fuel mixture that is produced by in-cylinder injector 110, rich in air-fuel ratio around the spark plug and in a stratified state are created in the combustion chamber. Even if the ignition timing at the spark plug is retarded to a large degree (for example, 15° ATDC), the fuel injection ratio of in-cylinder injector 110 is equal to or higher than the fuel injection ratio of intake manifold injector 120, thus the air-fuel ratio of the air-fuel mixture around the spark plug is richer, and this air-fuel mixture around the spark plug is surrounded by the homogeneous air-fuel mixture produced by intake manifold injector 120, so that flame can be propagated in a favorable state. Thus, flame is smoothly propagated and unburned fuel (HC) is unlikely to-be generated. The large retard of the ignition timing allows the exhaust temperature to increase.

Through the rapid catalyst warm-up as described above, the fact that some fuel injected from intake manifold injector 120 sticks to the port's wall surface due to the cold intake port can be taken into consideration to make a correction for increase to the quantity of fuel injected from intake manifold injector 120, by changing the DI ratio r, without increasing the total fuel quantity.

As described above, when the engine of a vehicle having the engine ECU of the present embodiment is started and rapid warm-up of the exhaust cleaning catalyst is necessary, the ratio of fuel injection by the in-cylinder injector is set to be equivalent to or higher than the ratio of fuel injection by the intake manifold injector. Accordingly, in the combustion chamber, an air-fuel mixture that is generated by the intake manifold injector, entirely lean in air-fuel ratio and in a homogeneous state as well as an air-fuel mixture that is generated by the in-cylinder injector, rich in air-fuel ratio around the spark plug and in a stratified state can be produced. At this time, the air-fuel ratio around the spark plug can be made richer. Since the air-fuel mixture around the spark plug is homogeneous (semi-stratified), flame propagation is facilitated and unburned fuel (HC) is unlikely to be generated. In such a state, the ignition timing is retarded to a large degree to enable the exhaust cleaning catalyst to be warmed up more rapidly as compared with the conventional art.

In this case, when the temperature of the engine is low and accordingly the rapid catalyst warm-up is performed, some fuel injected from the intake manifold injector into the low-temperature intake port sticks to the wall surface of the intake port, and the atomization state is thus unfavorable. Under this situation, usually, the amount of fuel sticking to the wall surface is added to the quantity of fuel to be injected from the intake manifold injector to inject fuel to the intake manifold, resulting in an increase in total fuel quantity (the sum of the quantity of fuel from the in-cylinder injector and the quantity of fuel from the intake manifold injector). Here, the fuel injection ratio of the in-cylinder injector is lowered while the fuel injection ratio of the intake manifold injector is increased to increase the quantity of fuel injected from the intake manifold injector. Thus, the fuel is injected in consideration of the fuel sticking to the wall surface. This is only a change in fuel injection ratio and the total quantity of fuel does not change, so that deterioration in fuel economy and exhaust components can be avoided. Accordingly, the rapid warm-up of the exhaust cleaning catalyst at the start of the engine in a cold state that has the in-cylinder injector and the intake manifold injector can be performed in a favorable manner while the total fuel quantity can be prevented from increasing in consideration of fuel sticking to the wall surface in the cold state.

<Decrease of Cold-State Increase Correction Value Q (P)>It is necessary to cancel the cold-state increase correction value Q (P) used for the increase (namely, set the cold-state increase correction value Q (P) to zero as the time passes), since the temperature of the intake port increases as the temperature of engine 10 increases (as the time passes after the start of engine 10). How this cancellation is made is described below. In the following description, the degree to which the cold-state increase correction value Q (P) is decreased per unit time is referred to as “attenuation ratio.”

As the temperature of engine 10 is higher (as the degree to which the temperature of engine 10 increases is larger), there is a smaller degree to which the amount of fuel sticking to the wall surface of the intake port has to be considered. Therefore, as the temperature of engine 10 is higher, or the degree to which the temperature of engine 10 increases is larger, the attenuation ratio is set to be higher, as shown in FIG. 5. In FIG. 5, as the attenuation ratio is higher with respect to the passage of time, the original state is reached earlier. In the example shown in FIG. 5, the decrease corresponding to 0.2 that is the cold-state increase correction value Q (P) of intake manifold injector 120 is made. Accordingly, the quantity of fuel injected from in-cylinder injector 110 is 0.45 while the quantity of fuel injected from intake manifold injector 120 is 0.15 and thus the DI ratio r is 75%. The example shown in FIG. 5 has the characteristic that the cold-state increase correction value Q (P) is decreased from only the fuel quantity injected from the intake manifold injector 120.

Alternatively, as shown in FIG. 6, the DI ratio r (=56%) in the case where the increase corresponding to the cold-state increase correction value Q (P) is made may be maintained while the quantity 0.2 that is the cold-state increase correction value Q (P) may be decreased. Accordingly, the quantity of fuel injected from in-cylinder injector 110 is 0.336 and the quantity of fuel injected from intake manifold injector 120 is 0.264 and the DI ratio r is still kept at 56%. In other words, the example shown in FIG. 6 has the characteristic that the fuel injection ratio of in-cylinder injector 110 to that of intake manifold injector 120 is decreased while maintaining the DI ratio (r=56%) that is set in consideration of the cold-state increase correction value Q (P).

Sill alternatively, as shown in FIG. 7, a decrease corresponding to the cold-state increase correction value Q (P) of 0.20 may be made while the DI ratio r is returned to the original one (=65%) before the increase corresponding to the cold-state increase correction value Q (P) is made. Accordingly, the quantity of fuel injected from in-cylinder injector 110 is 0.39 and the quantity of fuel injected from intake manifold injector 120 is 0.21 and the DI ratio r is returned to 65%. In other words, the example shown in FIG. 7 has the characteristic that the fuel injection ratio of in-cylinder injector 110 to that of intake manifold injector 120 is decreased such that the injection ratio is the one before the cold-state increase correction value Q (P) is taken into consideration.

It is noted that while respective examples shown in FIGS. 5 to 7 have the total fuel quantity of 0.60, the total fuel quantity is not restricted to 0.60. Further, the DI ratio is not restricted to any of those in respective examples shown in FIGS. 5 to 7 and may be controlled, for example, based on the fuel injection map or the like of engine 10 described hereinlater.

Thus, as shown in FIGS. 5 to 7, as the engine 10 is higher in temperature, or the degree to which the temperature of engine 10 changes is larger, the degree to which the fuel sticking to the wall surface has to be considered is smaller. Therefore, in such a case, the attenuation ratio is increased to allow the original state to be reached earlier.

<Engine (1) to which Present Control Apparatus is Suitably Applied>

An engine (1) to which the control apparatus of the present embodiment is suitably applied will be described hereinafter.

Referring to FIGS. 8 and 9, maps indicating a fuel injection ratio (hereinafter, also referred to as DI ratio r or simply as r) between in-cylinder injector 110 and intake manifold injector 120, identified as information associated with an operation state of engine 10, will now be described. The maps are stored in an ROM 320 of an engine ECU 300. FIG. 8 is the map for a warm state of engine 10, and FIG. 9 is the map for a cold state of engine 10.

In the maps of FIGS. 8 and 9, the fuel injection ratio of in-cylinder injector 110 is expressed in percentage as the DI ratio r, wherein the engine speed of engine 10 is plotted along the horizontal axis and the load factor is plotted along the vertical axis.

As shown in FIGS. 8 and 9, the DI ratio r is set for each operation region that is determined by the engine speed and the load factor of engine 10. “DI RATIO r=100%” represents the region where fuel injection is carried out from in-cylinder injector 110 alone, and “DI RATIO r=0%” represents the region where fuel injection is carried out from intake manifold injector 120 alone. “DI RATIO r≠0%”, “DI RATIO r≠100%” and “0% <DI RATIO r<100%” each represent the region where in-cylinder injector 110 and intake manifold injector 120 partake in fuel injection. Generally, in-cylinder injector 110 contributes to an increase of power performance, whereas intake manifold injector 120 contributes to uniformity of the air-fuel mixture. These two types of injectors having different characteristics are appropriately selected depending on the engine speed and the load factor of engine 10, so that only homogeneous charge combustion is conducted in the normal operation state of engine 10 (for example, a catalyst warm-up state during idling is one example of an abnormal operation state).

Further, as shown in FIGS. 8 and 9, the DI ratio r of in-cylinder injector 110 and intake manifold injector 120 is defined individually in the maps for the warm state and the cold state of the engine. The maps are configured to indicate different control regions of in-cylinder injector 110 and intake manifold injector 120 as the temperature of engine 10 changes. When the temperature of engine 10 detected is equal to or higher than a predetermined temperature threshold value, the map for the warm state shown in FIG. 8 is selected; otherwise, the map for the cold state shown in FIG. 9 is selected. In-cylinder injector 110 and/or intake manifold injector 120 are controlled based on the engine speed and the load factor of engine 10 in accordance with the selected map.

The engine speed and the load factor of engine 10 set in FIGS. 8 and 9 will now be described. In FIG. 8, NE(1) is set to 2500 rpm to 2700 rpm, KL(1) is set to 30% to 50%, and KL(2) is set to 60% to 90%. In FIG. 9, NE(3) is set to 2900 rpm to 3100 rpm. That is, NE(1)<NE(3). NE(2) in FIG. 8 as well as KL(3) and KL(4) in Fig. are also set appropriately.

In comparison between FIG. 8 and FIG. 9, NE(3) of the map for the cold state shown in FIG. 9 is greater than NE(1) of the map for the warm state shown in FIG. 8. This shows that, as the temperature of engine 10 becomes lower, the control region of intake manifold injector 120 is expanded to include the region of higher engine speed. That is, in the case where engine 10 is cold, deposits are unlikely to accumulate in the injection hole of in-cylinder injector 110 (even if fuel is not injected from in-cylinder injector 110). Thus, the region where fuel injection is to be carried out using intake manifold injector 120 can be expanded, whereby homogeneity is improved.

In comparison between FIG. 8 and FIG. 9, “DI RATIO r=100%” is shown in the region where the engine speed of engine 10 is NE(1) or higher in the map for the warm state, and in the region where the engine speed is NE(3) or higher in the map for the cold state. In terms of load factor, “DI RATIO r=100%” is shown in the region where the load factor is KL(2) or greater in the map for the warm state, and in the region where the load factor is KL(4) or greater in the map for the cold state. This means that in-cylinder injector 110 alone is used in the region of a predetermined high engine speed, and in the region of a predetermined high engine load. That is, in the high speed region or the high load region, even if fuel injection is carried out through in-cylinder injector 110 alone, the engine speed and the load of engine 10 are so high and the intake air quantity so sufficient that it is readily possible to obtain a homogeneous air-fuel mixture using only in-cylinder injector 110. In this manner, the fuel injected from in-cylinder injector 110 is atomized in the combustion chamber involving latent heat of vaporization (or, absorbing heat from the combustion chamber). Thus, the temperature of the air-fuel mixture is decreased at the compression end, so that the anti-knocking performance is improved. Further, since the temperature in the combustion chamber is decreased, intake efficiency is improved, leading to high power.

In the map for the warm state in FIG. 8, fuel injection is also carried out using in-cylinder injector 110 alone when the load factor is KL(1) or less. This shows that in-cylinder injector 110 alone is used in a predetermined low-load region when the temperature of engine 10 is high. When engine 10 is in the warm state, deposits are likely to accumulate in the injection hole of in-cylinder injector 110. However, when fuel injection is carried out using in-cylinder injector 110, the temperature of the injection hole can be lowered, in which case accumulation of deposits is prevented. Further, clogging at in-cylinder injector 110 may be prevented while ensuring the minimum fuel injection quantity thereof. Thus, in-cylinder injector 110 solely is used in the relevant region.

In comparison between FIG. 8 and FIG. 9, the region of “DI RATIO r=0%” is present only in the map for the cold state of FIG. 9. This shows that fuel injection is carried out through intake manifold injector 120 alone in a predetermined low-load region (KL(3) or less) when the temperature of engine 10 is low. When engine 10 is cold and low in load and the intake air quantity is small, the fuel is less susceptible to atomization. In such a region, it is difficult to ensure favorable combustion with the fuel injection from in-cylinder injector 110. Further, particularly in the low-load and low-speed region, high power using in-cylinder injector 110 is unnecessary. Accordingly, fuel injection is carried out through intake manifold injector 120 alone, without using in-cylinder injector 110, in the relevant region.

Further, in an operation other than the normal operation, or, in the catalyst warm-up state during idling of engine 10 (an abnormal operation state), in-cylinder injector 110 is controlled such that stratified charge combustion is effected. By causing the stratified charge combustion only during the catalyst warm-up operation, warming up of the catalyst is promoted to improve exhaust emission.

<Engine (2) to which Present Control Apparatus is Suitably Applied>

An engine (2) to which the control apparatus of the present embodiment is suitably applied will be described hereinafter. In the following description of the engine (2), the configurations similar to those of the engine (1) will not be repeated.

Referring to FIGS. 10 and 11, maps indicating the fuel injection ratio between in-cylinder injector 110 and intake manifold injector 120, identified as information associated with the operation state of engine 10, will be described. The maps are stored in ROM 320 of an engine ECU 300. FIG. 10 is the map for the warm state of engine 10, and FIG. 11 is the map for the cold state of engine 10.

FIGS. 10 and 11 differ from FIGS. 8 and 9 in the following points. “DI RATIO r=100%” holds in the region where the engine speed of engine 10 is equal to or higher than NE(1) in the map for the warm state, and in the region where the engine speed is NE(3) or higher in the map for the cold state. Further, “DI RATIO r=100%” holds in the region, excluding the low-speed region, where the load factor is KL(2) or greater in the map for the warm state, and in the region, excluding the low-speed region, where the load factor is KL(4) or greater in the map for the cold state. This means that fuel injection is carried out through in-cylinder injector 110 alone in the region where the engine speed is at a predetermined high level, and that fuel injection is often carried out through in-cylinder injector 11O alone in the region where the engine load is at a predetermined high level. However, in the low-speed and high-load region, mixing of an air-fuel mixture produced by the fuel injected from in-cylinder injector 110 is poor, and such inhomogeneous air-fuel mixture within the combustion chamber may lead to unstable combustion. Thus, the fuel injection ratio of in-cylinder injector 110 is to be increased as the engine speed increases where such a problem is unlikely to occur, whereas the fuel injection ratio of in-cylinder injector 110 is to be decreased as the engine load increases where such a problem is likely to occur. These changes in the DI ratio r are shown by crisscross arrows in FIGS. 10 and 11. In this manner, variation in output torque of the engine attributable to the unstable combustion can be suppressed. It is noted that these measures are substantially equivalent to the measures to decrease the fuel injection ratio of in-cylinder injector 110 in connection with the state of the engine moving towards the predetermined low speed region, or to increase the fuel injection ratio of in-cylinder injector 110 in connection with the engine state moving towards the predetermined low load region. Further, in a region other than the region set forth above (indicated by the crisscross arrows in FIGS. 10 and 11) and where fuel injection is carried out using only in-cylinder injector 110 (on the high speed side and on the low load side), the air-fuel mixture can be readily set homogeneous even when the fuel injection is carried out using only in-cylinder injector 110. In this case, the fuel injected from in-cylinder injector 110 is atomized in the combustion chamber involving latent heat of vaporization (by absorbing heat from the combustion chamber). Accordingly, the temperature of the air-fuel mixture is decreased at the compression end, whereby the antiknock performance is improved. Further, with the decreased temperature of the combustion chamber, intake efficiency is improved, leading to high power output.

In engine 10 described in conjunction with FIGS. 8-11, homogeneous charge combustion is realized by setting the fuel injection timing of in-cylinder injector 110 in the intake stroke, while stratified charge combustion is realized by setting it in the compression stroke. That is, when the fuel injection timing of in-cylinder injector 110 is set in the compression stroke, a rich air-fuel mixture can be located locally around the spark plug, so that a lean air-fuel mixture in totality is ignited in the combustion chamber to realize the stratified charge combustion. Even if the fuel injection timing of in-cylinder injector 110 is set in the intake stroke, stratified charge combustion can be realized if a rich air-fuel mixture can be located locally around the spark plug.

As used herein, the stratified charge combustion includes both the stratified charge combustion and semi-stratified charge combustion set forth below. In the semi-stratified charge combustion, intake manifold injector 120 injects fuel in the intake stroke to generate a lean and homogeneous air-fuel mixture in the whole combustion chamber, and then in-cylinder injector 110 injects fuel in the compression stroke to generate a rich air-fuel mixture around the spark plug, so as to improve the combustion state. Such a semi-stratified charge combustion is preferable in the catalyst warm-up operation for the following reasons. In the catalyst warm-up operation, it is necessary to considerably retard the ignition timing and maintain a favorable combustion state (idling state) so as to cause a high-temperature combustion gas to arrive at the catalyst. Further, a certain quantity of fuel must be supplied. If the stratified charge combustion is employed to satisfy these requirements, the quantity of fuel will be insufficient. With the homogeneous charge combustion, the retarded amount for the purpose of maintaining favorable combustion is small as compared to the case of stratified charge combustion. For these reasons, the above-described semi-stratified charge combustion is preferably employed in the catalyst warm-up operation, although either of stratified charge combustion and semi-stratified charge combustion may be employed.

Further, in the engine described in conjunction with FIGS. 8-11, the fuel injection timing by in-cylinder injector 110 is preferably set in the compression stroke for the reason set forth below. It is to be noted that, for most of the fundamental region (here, the fundamental region refers to the region other than the region where semi-stratified charge combustion is carried out with fuel injection from intake manifold injector 120 in the intake stroke and fuel injection from in-cylinder injector 110 in the compression stroke, which is carried out only in the catalyst warm-up state), the fuel injection timing of in-cylinder injector 110 is set at the intake stroke. The fuel injection timing of in-cylinder injector 110, however, may be set temporarily in the compression stroke for the purpose of stabilizing combustion, as will be described hereinafter.

When the fuel injection timing of in-cylinder injector 110 is set in the compression stroke, the air-fuel mixture is cooled by the fuel injection during the period where the temperature in the cylinder is relatively high. This improves the cooling effect and, hence, the antiknock performance. Further, when the fuel injection timing of in-cylinder injector 110 is set in the compression stroke, the time required starting from fuel injection up to the ignition is short, so that the air current can be enhanced by the atomization, leading to an increase of the combustion rate. With the improvement of antiknock performance and the increase of combustion rate, variation in combustion can be obviated to allow improvement in combustion stability.

Furthermore, regardless of the temperature of engine 10 (namely regardless of whether the engine state is the warm state or the cold state), the map for the warm state shown in FIG. 8 or 10 may be used in an off-idle state (when the idle switch is OFF, when the accelerator pedal is depressed) (i.e., regardless of whether the engine state is the cold state or the warm state, in-cylinder injector 100 is used for the low-load region).

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

1. A control apparatus for an internal combustion engine including a first fuel injection mechanism injecting fuel into a cylinder, a second fuel injection mechanism injecting fuel into an intake manifold, and an ignition device, said internal combustion engine having an exhaust system provided with a catalyst that is used for cleaning exhaust and that is activated at a temperature of at least a predetermined temperature, said control apparatus comprising: a detection unit detecting a request to warm up said catalyst; a control unit controlling said first and second fuel injection mechanisms, based on conditions required of said internal combustion engine, such that said first and second fuel injection mechanisms partake in fuel injection; an ignition control unit controlling said ignition device; and a temperature detector detecting the temperature of said internal combustion engine, wherein said control unit controls said first and second fuel injection mechanisms, considering the temperature of said internal combustion engine, such that the ratio of fuel injection by said first fuel injection mechanism is at least equal to the ratio of fuel injection by said second fuel injection mechanism under the conditions that said first and second fuel injection mechanisms partake in the fuel injection and said request to warm up is detected, and said ignition control unit controls said ignition device to retard ignition timing when said request to warm up is detected.
 2. The control apparatus for an internal combustion engine according to claim 1, said control apparatus further comprising a calculation unit calculating, based on the temperature of said internal combustion engine, an amount of wall-sticking fuel that is an amount of fuel injected by said second fuel injection mechanism into said intake manifold and sticking to a wall surface, wherein said control unit controls, considering said amount of wall-sticking fuel, said first and second fuel injection mechanisms.
 3. The control apparatus for an internal combustion engine according to claim 2, wherein said control unit changes, considering said amount of wall-sticking fuel, the ratio of fuel injection between said first fuel injection mechanism and said second fuel injection mechanism by increasing the ratio of fuel injection by said second fuel injection mechanism.
 4. The control apparatus for an internal combustion engine according to claim 2, wherein said control unit changes the ratio of fuel injection between said first fuel injection mechanism and said second fuel injection mechanism by making an increase correction to the quantity of injected fuel injected by said second fuel injection mechanism according to said amount of wall-sticking fuel and increasing the ratio of fuel injection by said second fuel injection mechanism.
 5. The control apparatus for an internal combustion engine according to claim 4, said control apparatus further comprising a decrease unit attenuating, based on the temperature of said internal combustion engine, the quantity of injected fuel which is injected by said second fuel injection mechanism and to which said increase correction is made.
 6. The control apparatus for an internal combustion engine according to claim 5, wherein said decrease unit more sharply attenuates the quantity of injected fuel to which said increase correction is made, as the temperature of said internal combustion engine is higher.
 7. The control apparatus for an internal combustion engine according to claim 5, wherein said decrease unit more slowly attenuates the quantity of injected fuel to which said increase correction is made, as the temperature of said internal combustion engine is lower.
 8. The control apparatus for an internal combustion engine according to claim 5, wherein said decrease unit decreases, from the quantity of injected fuel injected by said second fuel injection mechanism, the quantity of fuel corresponding to said increase correction.
 9. The control apparatus for an internal combustion engine according to claim 5, wherein said decrease unit decreases, from the quantity of injected fuel injected by said first fuel injection mechanism and from the quantity of injected fuel injected by said second fuel injection mechanism, the quantity of fuel corresponding to said increase correction.
 10. The control apparatus for an internal combustion engine according to claim 5, wherein said decrease unit decreases the quantity of fuel corresponding to said increase correction, such that the ratio of fuel injection between said first fuel injection mechanism and said second fuel injection mechanism before said increase correction is made is maintained.
 11. The control apparatus for an internal combustion engine according to claim 5, wherein said decrease unit decreases the quantity of fuel corresponding to said increase correction, such that the ratio of fuel injection between said first fuel injection mechanism and said second fuel injection mechanism after said increase correction is made is maintained.
 12. The control apparatus for an internal combustion engine according to claim 2, wherein said control unit controls said first and second fuel injection mechanisms such that the sum of the quantity of injected fuel injected by said first fuel injection mechanism and the quantity of injected fuel injected by said second fuel injection mechanism in the case where said amount of wall-sticking fuel is considered is smaller than that in the case where said amount of wall-sticking fuel is not considered.
 13. The control apparatus for an internal combustion engine according to claim 1, wherein said first fuel injection mechanism is an in-cylinder injector and said second fuel injection mechanism is an intake manifold injector.
 14. A control apparatus for an internal combustion engine including first fuel injection means for injecting fuel into a cylinder, second fuel injection means for injecting fuel into an intake manifold, and an ignition device, said internal combustion engine having an exhaust system provided with a catalyst that is used for cleaning exhaust and that is activated at a temperature of at least a predetermined temperature, said control apparatus comprising: detection means for detecting a request to warm up said catalyst; control means for controlling said first and second fuel injection means, based on conditions required of said internal combustion engine, such that said first and second fuel injection means partake in fuel injection; ignition control means for controlling said ignition device; and temperature detection means for detecting the temperature of said internal combustion engine, wherein said control means includes means for controlling said first and second fuel injection means, considering the temperature of said internal combustion engine, such that the ratio of fuel injection by said first fuel injection means is at least equal to the ratio of fuel injection by said second fuel injection means under the conditions that said first and second fuel injection means partake in the fuel injection and said request to warm up is detected, and said ignition control means includes means for controlling said ignition device to retard ignition timing when said request to warm up is detected.
 15. The control apparatus for an internal combustion engine according to claim 14, said control apparatus further comprising calculation means for calculating, based on the temperature of said internal combustion engine, an amount of wall-sticking fuel that is an amount of fuel injected by said second fuel injection means into said intake manifold and sticking to a wall surface, wherein said control means includes means for controlling, considering said amount of wall-sticking fuel, said first and second fuel injection means.
 16. The control apparatus for an internal combustion engine according to claim 15, wherein said control means includes means for changing, considering said amount of wall-sticking fuel, the ratio of fuel injection between said first fuel injection means and said second fuel injection means by increasing the ratio of fuel injection by said second fuel injection means.
 17. The control apparatus for an internal combustion engine according to claim 15, wherein said control means includes means for changing the ratio of fuel injection between said first fuel injection means and said second fuel injection means by making an increase correction to the quantity of injected fuel injected by said second fuel injection means according to said amount of wall-sticking fuel and increasing the ratio of fuel injection by said second fuel injection means.
 18. The control apparatus for an internal combustion engine according to claim 17, said control apparatus further comprising decrease means for attenuating, based on the temperature of said internal combustion engine, the quantity of injected fuel which is injected by said second fuel injection means and to which said increase correction is made.
 19. The control apparatus for an internal combustion engine according to claim 18, wherein said decrease means includes means for more sharply attenuating the quantity of injected fuel to which said increase correction is made, as the temperature of said internal combustion engine is higher.
 20. The control apparatus for an internal combustion engine according to claim 18, wherein said decrease means includes means for more slowly attenuating the quantity of injected fuel to which said increase correction is made, as the temperature of said internal combustion engine is lower.
 21. The control apparatus for an internal combustion engine according to claim 18, wherein said decrease means includes means for decreasing, from the quantity of injected fuel injected by said second fuel injection means, the quantity of fuel corresponding to said increase correction.
 22. The control apparatus for an internal combustion engine according to claim 18, wherein said decrease means includes means for decreasing, from the quantity of injected fuel injected by said first fuel injection means and from the quantity of injected fuel injected by said second fuel injection means, the quantity of fuel corresponding to said increase correction.
 23. The control apparatus for an internal combustion engine according to claim 18, wherein said decrease means includes means for decreasing the quantity of fuel corresponding to said increase correction, such that the ratio of fuel injection between said first fuel injection means and said second fuel injection means before said increase correction is made is maintained.
 24. The control apparatus for an internal combustion engine according to claim 18, wherein said decrease means includes means for decreasing the quantity of fuel corresponding to said increase correction, such that the ratio of fuel injection between said first fuel injection means and said second fuel injection means after said increase correction is made is maintained.
 25. The control apparatus for an internal combustion engine according to claim 15, wherein said control means includes means for controlling said first and second fuel injection means such that the sum of the quantity of injected fuel injected by said first fuel injection means and the quantity of injected fuel injected by said second fuel injection means in the case where said amount of wall-sticking fuel is considered is smaller than that in the case where said amount of wall-sticking fuel is not considered.
 26. The control apparatus for an internal combustion engine according to claim 14, wherein said first fuel injection means is an in-cylinder injector and said second fuel injection means is an intake manifold injector. 